Gameplay Issues
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Got some replacement 2.5SB fuses for the solenoids, put one in and started a game, pressing both of the flipper buttons together causes the game to reset. Did a quick google and suggestions to fix this included removing and reconnecting the power connector to the MPU and also replacing the large filter cap on the power PCB at C10. Checked the power PCB and say that the filter cap had already been replaced at some point so attempted the remove and reinstall connector on the MPU option, this appears to have fixed the issue with resets when both flipper buttons pressed.
Started a game and drained the first ball, the solenoid fired the ball back into the ball ramp but the end of ball sequence didnt start, outhole switch must be working as it triggered the solenoid, checked playfield behaviour and found that both lower drop target banks no longer register along with the 2 kickouts on the upper playfield, other targets rollovers and the upper drop targets all seem to be registering correctly and still scoring while the game is like this, so the CPU is still running, very strange. Checking the switch matrix all the drops and kickouts are on the same columns. Back out with the logic probe and started another game, drop targets and kickouts all work ok until the ball drains and the same thing happens, try the logic probe on the switch column outputs and find all are strobing ok so dont think its an issue with the switch PIA as they all also register ok until the first ball drains. Keep hitting random switches on the playfield and can sometimes seem to trigger the end of ball sequence so the game moves onto the next ball, although ball in play display is not advancing correctly, but not sure if I started a 2 player game or not. Also tried with a 2+ player game to see and it still gives the same behaviour.
Decided to have a check of voltages in the backbox, checked the 5v logic on the power PCB and seems to be outputting around 4.97v which I read should be enough, also checked at the 5v test point on the MPU and voltage still the same there as well.
Noticed something odd with the the test point for the memory protect coindoor lockout switch, manual says this should show ~5v when closed but only getting 3.4v, need to do some more checks on the MPU for voltages.
Another thing noticed, ran the diag test on the MPU and it flashes 0 and then goes off suggesting everything testing ok, there is also an enter button above the diag button that can't seem to find any mention in manual about its purpose, pressing and holding displays 3 on the diag LED which would point to a ROM issue but not sure if that's the correct purpose.